Upgraded cast refractory products

ABSTRACT

THE INVENTION RELATED TO CAST REFRACTORY PRODUCTS HAVING DISPERSED SHRINKAGE CAVITIES OR VOIDS, THESE PRODUCTS BEING CHARACTERIZED IN THAT SAID CAVITIES OR VOIDS ARE FILLED WITH A SUITABLE GREOUT COMPRISING POWDERED REFRACTORY MATERIALS.

United States Patent US. Cl. 117-Z R 6 Claims ABSTRACT OF THE DISCLOSUREThe invention relates to cast refractory products having dispersedshrinkage cavities or voids, these products being characterized in thatsaid cavities or voids are filled with a suitable grout comprisingpowdered refractory materials.

Electrically fused, cast refractory products are wellknown materialswhich are used, more especially in various industries, for theconstruction of certain parts of furnaces. Some of these products havethe tendency, during their manufacture to give rise to a quiteconsiderable shrinkage cavity or pipe, and it is customary to dispersethe latter.

A typical example of these materials is the product sold commerciallyunder the name of Corhart 104 and described in United States patentspecification No. 2,599,566, for which a typical composition is: 55-56%of MgO, 20% of Cr O 12-13% of FeO, 7-8% of A1 0 2.5% of Si0 and 1.3% ofCaO. This product is manufactured in the form of slabs, from which thecommercial units are cut.

For these products, the dispersion of the shrinkage cavity is achievedby means of various well-known procedures, such as the introduction intothe casting of the slabs of a certain amount of a small-grain substancemade up of the materal crushed up (a method described on page 247 of theEnglish translation of the book by A. A. Litwakovskii: Fused CastRefractories, 1961, or in French patent specification No. 738,117), orsuch as the introduction into the casting of the slabs of a product ableto liberate gases (a method described in French patent specification No.922,954), or in a combination of these methods.

This method of proceeding has a twofold result:

In respect of the economic effect, it makes it possible to cut from theslabs units suitable over almost their entire height, and to re-usedefective units in the form of small grains; and

In respect of quality, it renders the quality homogeneous over almostthe entire height of the slabs and, through the introduction of holesdue to the distribution of the shrinkage cavity, to improve resistanceto thermal fracturing in the material.

Holes formed in this way at the time of the dispersion of the shrinkagecavity are not Without drawbacks, however; they spoil the appearance ofthe product, constitute relatively easier paths for the penetration ofaggressive agents and, when the refractory is in contact with fluids inmovement, give rise to turbulences and vortices which hasten the wearingdown of the material.

The sole means hitherto known and employed for obviating these drawbackswas to bring compact blocks into being, but the improvement in theresistance to cor- 3,667,981 Patented June 6, 1972 ice rosion obtainedin this way was counter-balanced in respect of quality by a decreasedresistance to thermal variations and, in respect of economic effect, byso great an increase in the costs of manufacture that the profitabilityof the product was no longer assured.

The present invention has for its object electrically fused, castrefractory products of improved appearance and quality, and themanufacturing cost of which is slightly less than that of products atpresent available.

According to the invention, the said refractory products arecharacterized in that the holes from the dispersed shrinkage cavity arefilled in and made good by means of a suitable grout.

The filling-in and making good of the holes from the dispersed shrinkagecavity can be put into effect by various methods.

One of these methods consists in subjecting the block to be filled in(the sawn faces of which have been arranged horizontally) to horizontalvibrations or to vertical shocks, and to apply the grout with a trowelsuccessively to the two sawn faces.

Another of the said methods consists in arranging the block requiring tobe filled in in a chamber which can be de-pressurized, creating a vacuumin the said chamber, placing the chamber in communication with a sourceof grouting material while preventing the entry of air into the chamberso as to introduce the grout into the chamber and to fill the holes withgrout, then interrupting the vacuum, removing the block, scraping itover and in recovering the remaining grout for the following operation.The block is then allowed to dry in the air or under any otherappropriate conditions.

A further possible method consists in arranging the block to be filledin in a chamber which can be linked to a pressure source, introducingthe grout into the chamber, and placing the chamber under pressure,after which the pressure is relieved, the block is removed and isscraped over, as in the previous instance. This method can moreover beusefully combined with the preceding one, it being possible to effectthe pressurization of the chamber after the introduction in vacuo of thegrout. It is this latter method which constitutes the best way orfilling in the refractory products which are the aim of the invention.

The conditions as regards vacuum and pressure are not critical. It ispossible, for instance, to apply a vacuum of the order of 10 to 50 mm.of Hg by means of an impeller pump, and/or a pressure of the order ofseveral atmospheres by making a connection to a source of compressedair.

The grout employed should naturally satisfy a number of conditions. Inparticular, it should not pour out excessively under the effect of thevibrations or shocks in question or of the suction of the liquid by thevacuum: it should be sufliciently fine to pentrate into the narroworifices of the refractory product requiring treatment, but should notbe too fine, so as to prevent too great a contraction upon drying; itshould be thixotropic, so as not to run out of the external shrinkageholes after the treatment; it should not harden too rapidly in thepresence of cold; it should harden in the presence of heat, so as not tocollapse into powder at the commencement of the heating process whenactually in use; it should be adequately resistant to corrosion. Variousexamples of grout will be given hereinafter.

The filling-in and making good of the dispersed shrinkage holes is, inthe case of a method for filling in and making good and for a givengrout, all the better, the more extensive the communication between theholes is. Thus, though slabs of Corhart 104 prepared by the normalprocedure may be treated in accordance with the invention so as toobtain slabs of improved quality, the present applicant has found thatbetter results are achieved when the slabs are manufactured by a specialmethod which leads to the formation of an open porosity in the finalslabs. Such a method, for example, consists in dispersing the shrinkagecavity by the addition of smallgrain material and by employing a fusiontechnique which brings about degasification of the bath of meltedmaterial of the kind described in French patent specification No.1,208,577 and its addition, No. 75,893, 82,057, 82,310 and 84,153.

The refractory products according to the invention possess, in relationto the products whose dispersed shrinkage holes have not been filled in,an improved appearance, a density increased by approximately 5%, and aresistance to corrosion which is higher by about 15%. In another.connection, the treatment covered by the invention makes it possible todecrease the efiects of tur- The material concerned is the commercialproduct Corhart 104, pulverized and passing through a sieve o! 0.5 mm.mesh.

3 The material concerned is the commercial product Corhart 104,(pulverized irli1 an Alslng-Brand ball-mill and passing through a sieveof mm. mes

To these compositions was added to approximately of water in order toobtain grouts of the appropriate consistency.

EXAMPLE 2 The grout A and B of Example 1 were employed in the carryingout of tests on the filling-in eifect in respect of blocks of Corhart104 specially manufactured to obtain a degassed product.

The filling-in method employed and the results obtained are shown in thetable below. For each series of tests, the results have been classifiedaccording to increasing densities:

Densities in gJcm. Average Grout Gain, ain,

Test No. Method offilling-ln employed used Before After gJcm. gfcm.

2- Horizontal vibrations 1 A 3. 18 3. 27 0. 09 0. 08 3. 3. 24 3. 34 0.10 2. 97 3. 08 0. 11 3. 06 3. 20 O. 14 3. 15 3. 28 0. 13

Vacuum (12-15 mm. of Hg) B 3 14 3 25 u 0. 15 22 3.16 3.32 0.16 3.22 3.340.12

1 The block to be treated was placed on a frame set vibrating by apneumatic hammer 1 The block to be treated was subjected to shocks of anamplitude equal to 3 cm. and at a frequency of 160 shocks per minute.

EXAMPLE 1 The following table indicates the composition of the groutsemployed for filling in the cavities or holes in refractory productswith a base of chromium oxide and of magnesium oxide.

0f the three filling-in methods employed for the treat- 60 ment of theseblocks, the method in vacuo yields the best results, with an averagegain in density of 0.15 g./ cm. The gain does not appear to dependespecially on the initial density, but rather on the volume of theaccessible holes or cavities, one large hole filling up better thanseveral small ones.

In this series of tests, only the two first grouts A and B, with a largeproportion of C 104 powder, were used, to avoid contraction in the largeshrinkage holes. Grout B, which contains 1% of commercial clay, isslightly superior to grout A.

The blocks, duly filled in, are good enough to use.

EXAMPLE 3 Grouts A, B and C in Example 1 were used in carrying out testson filling in blocks of Corhart 104, of standcan be used, varying therelative proportion of C 104 powder, of Alsing C 104 and of slurriesoriginating in the sawing of the Corhart 104 slabs. Likewise, it ispossible to use grouts other than with a base of Corhart 104, forexample with a magnesia base.

Densities in g./ ems Average 'le Grout Gain, g./ gain, No Method offilling-in employed used Before After em. g./em.

i a. 02 3. s 0. O6 055 3. 13 3. 18 0. Vertical shocks B 3.15 3. 21 0.06

3. 18 3. 25 0. 07 0. 06 3. 27 3. 33 0. 06 g. 26 0.06 1 1 O. 10 B i a. asa. 39 0.06 i 03 Vacuum (12-15 mm. of Hg) 3. 27 3. 37 0.10 C 3. 28 3. 410. 13 0. 12

8. 3. 47 0. 12 }Pressure, (4.5 kgJcm. O g: 0.08

3.18 3. 35 0.17 3. 22 3. 33 0. 11 Vacuum (15 mm. of Hg) plus pressure(4.5 kg./cm. C 3. 23 3. 37 0.14 0. l4 3. 24 3. 38 0. 14 42 3. 24 3. 380. 14

l The block to be treated was subjected to shocks with an amplitudeequal to 3 cm. and with a frequency of 160 shocks per minute.

Comparison of the tables in Examples 2 and 3 clearly shows that, for oneand the same grout and the same method of filling in, the Corhart 104 ofspecial manufacture leads to better filling in.

In another connection, the table in Example 3 shows that the best methodof filling in is carried out in vacuo, followed by pressurization. GroutC with a finer grainsize is superior to grout B from the point of viewof penetration, as the results of tests 31 to 35 show. Grout C however,has the drawback of being more awkward and of suffering from greatercontraction upon being dried.

EXAMPLE 4 In place of grout C, which has certain drawbacks (a high costof manufacture and considerable contraction upon being dried), grout Dcan be employed. This grout was tried on blocks of special manufactureand, as in the other tests, the results have been classified byincreasing densities:

The products treated according to the invention possess increasedresistance to corrosion, as the results of the following laboratorytests show:

1 FeO, 30%; C210, and 810;, 20%.

-It is self-evident that the methods described for carrying theinvention into effect are only examples and that it would be possible tomodify them, more especially by substituting technically equivalentmeans, without however thereby going beyond the scope of the invention.

Grout Method of filling-in employed used Vacuum (15 mm. of Hg) pluspressure (4.5 kgJcm. D

Grout D leads to results which are slightly inferior to those with groutC (the average gain is the same, but the results given by grout C referto normal blocks, whereas whose of grout D relate to special blocks).Nevertheless, grout D constitutes the best comprise from the point ofview of quality/ cost of manufacture.

The aforementioned examples show that the size of the holes and theporosity of the blocks has a preponderating influence on the gain indensity achieved.

Naturally, other grouts can be used in place of the particular groutsindicated. In particular, intermediate grouts Densities in g./em. 3Average Gain, gain, Before After g./em 3 g./em. 3

00 We claim:

hardenable, thixotropic grout comprising, as main solid components,powdered refractory materials having a composition similar to that ofthe said refractory product.

3. Cast refractory products comprising, by weight, about 55-56% MgO,about 20% Cr O about 12-13% FeO, about 78% A1 about 2.5% Si0 and about1.3% Q10, and having dispersed shrinkage cavities therein, characterizedin that said cavities are filled with a heat hardenable, thixotropicgrout comprising, as main solid components, powdered refractorymaterials having a composition similar to that of the cast refractoryproducts.

4. Process for upgrading cast refractory products of any knownoxide-based composition having dispersed shrinkage cavities therein,characterized by filling said cavities with a heat-hardenable,thixotropic grout comprising, as main solid components, at least onepowdered refractory oxide selected among the main oxides contained inthe composition of said cast refractory products.

5. Process for upgrading cast refractory products of any knownoxide-based composition having dispersed shrinkage cavities therein,characterized by filling said cavities with a heat-hardena-ble,thixotropic grout comprising, as main solid components, powderedrefractory materials having a composition similar to that of the castrefractory product.

6. Process for upgrading cast refractory products comprising, by Weight,about -56% MgO, about 20% Cr O about 12-13% FeO, about 7-8% A1 0 aboutReferences Cited UNITED STATES PATENTS 707,670 8/1902 Zuckschwerdt117-123 A 2,968,083 1/1962 Lentz et a1 117-2 R 3,141,790 7/1964 Davieset al 117123 A 2,534,328 12/1950 Whitman 117--169 R 2,187,324 1/1940Many 1172 R ALFRED L. LEAVITI, Primary Examiner M. F. ESPOSITO,Assistant Examiner US. Cl. X.R.

